> Stone is an incredibly efficient thermal material which is why animals and humans have lived in caves for thousands of years.

Most stone makes for a pretty bad insulator. But the ground, in aggregate, is a great insulator and has very very large thermal mass. So you can go in a hole that’s more than a few feet underground, and the temperature is fairly constant.

They also died in caves for thousands of years. They lived there because it was the best shelter available, not because it was the ideal shelter.